Patch antennas are increasingly being used in wireless applications. Due to a patch antenna's low profile, it can easily be made to conform to a host surface. Also, the patch antenna can have many geometries, such as, for example, circular or rectangular geometry. A patch antenna includes a base conductor layer (the ground plane), a dielectric spacer (the substrate), and a signal conductor layer (the patch). A feed line (e.g., micro-strip line or coaxial line) electromagnetically connects the signal conductor layer and the ground plane to a transmitter and/or a receiver.
Conventional patch antennas, however, suffer from several disadvantages, including narrow bandwidth. Patch antennas radiate because of the fringing fields between the patch edge and the ground plane. For good performance, a thick dielectric substrate having a low dielectric constant is desirable since this provides larger bandwidth and better radiation. A patch antenna with a wide bandwidth typically has a large profile due to the height above the ground plane required to achieve this bandwidth, making a wideband patch antenna infeasible in many applications.
Recently, patch antenna arrays have been used in Wi-Fi and WiMAX applications. Array antennas offer high gain and high system capacity. However, existing patch antenna arrays have large antenna size and narrow frequency bandwidth due to restrictions in PCB substrate thickness.
In Wi-Fi and WiMAX base station applications, high gain array antennas with dual polarization are required to decrease the number of antennas and improve wireless system performance. Some array antennas utilize horizontal and vertical polarizations to achieve polarization diversity. The dual-polarized antenna can offer two transmission channels in the same frequency band. However, it is difficult to achieve wide bandwidth in dual polarized antennas.
A number of dual-polarized array antennas have been proposed for Wi-Fi and WiMAX applications. One proposed antenna array comprises two substrate layers which are separated by an air gap. The existence of an air gap between the two substrate layer causes the antenna to be less rigid and difficult to manufacture.
Another proposed antenna array comprises a single substrate layer, a radiation layer, and conical elements. An air gap exists between the conical elements and the substrate. Because of the conical elements and the air gap, the antenna is difficult to manufacture and is less rigid.